Photoresist additive for preventing acid migration and photoresist composition comprising the same

ABSTRACT

Photoresist additives for preventing the acid generated in the exposed area during the course of a photolithography process from being diffused to the unexposed area, photoresist compositions containing the same, and a process for forming a photoresist pattern using the same. Photoresist compositions comprising the disclosed additive can prevent acid diffusion effectively even if the additive is used in low concentrations, thereby improving LER, resulting in excellent profiles and lowering optimum irradiation energies.  
                 
 
     wherein, R 1 , R 2 , R 3 , R 4  and k are as defined herein.

BACKGROUND

[0001] 1. Technical Field

[0002] Photoresist additives for preventing acid migration andphotoresist compositions containing the same are disclosed. Morespecifically, photoresist additives are disclosed which prevent acidgenerated in an exposed area during the course of a photolithographyprocess from diffusing or migrating to an unexposed area. Photoresistcompositions containing the same and a process for forming a photoresistpattern using the same are also disclosed.

[0003] 2. Description of the Related Art

[0004] Recently, chemical amplification-type DUV (deep ultra violet)photoresists have proven to be useful in achieving high sensitivity inprocesses for forming ultrafine patterns in the manufacture ofsemiconductors. These photoresists are prepared by blending a photoacidgenerator with a polymer matrix having acid labile structures.

[0005] According to the reaction mechanism of such a photoresist, thephotoacid generator generates acid when it is irradiated by the lightsource, and the main chain or branched chain of the polymer matrix inthe exposed or irradiated portion reacts with the generated acid and isdecomposed or cross-linked, so that the polarity of the polymer isconsiderably altered. This alteration of polarity results in asolubility difference in the developing solution between the irradiatedexposed area and the unexposed area, thereby forming a positive ornegative image of a mask on the substrate.

[0006] It is necessary to prevent acid generated in the exposed areaduring the course of a photolithography process from diffusing ormigrating to the unexposed area so as to improve resolution of theresulting pattern and to obtain a superior profile.

[0007] In order to prevent the acid diffusion, an amine or amidecompound has been added to a chemical amplification type photoresistcomposition with an amount ranging from 5 to 30% per mole of thephotoacid generator.

[0008] However, excessive use of amine or amide has caused lightabsorbance and optimum irradiation energy to increase, therebydeteriorating the productivity of the exposing process.

[0009] Moreover, a line edge roughness (hereinafter, abbreviated as‘LER’) between 10-20 nm has been commonly shown in forming photoresistpattern of 110 nm or less, leading to inefficiencies in the process andfinal products with reduced stability.

SUMMARY OF THE DISCLOSURE

[0010] Accordingly, photoresist additives are disclosed which canprevent diffusion of acid generated in the exposed area effectively.Photoresist compositions containing the same are also disclosed.

[0011] A process for forming an ultrafine pattern by using the disclosedphotoresist compositions and a semiconductor element manufacturedaccording to the disclosed process are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a photograph of a photoresist pattern obtained using theprocedure set forth in Example 1;

[0013]FIG. 2 is a photograph of a photoresist pattern obtained using theprocedure set forth in Example 2;

[0014]FIG. 3 is a photograph of a photoresist pattern obtained using theprocedure set forth in Example 3;

[0015]FIG. 4 is a photograph of a photoresist pattern obtained using theprocedure set forth in Example 4;

[0016]FIG. 5 is a photograph of a photoresist pattern obtained using theprocedure set forth in Comparative Example 1; and

[0017]FIG. 6 is a photograph of a photoresist pattern obtained using theprocedure set forth in Comparative Example 2.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0018] An additive for preventing acid diffusion is disclosed, whereinthe additive is represented by Formula 1:

[0019] wherein, R₁, R₂, R₃ and R₄ are individually selected from thegroup consisting of H and linear or branched C₁-C₁₀ alkyl, and k is 0 or1.

[0020] The above compound of Formula 1 can also be represented byFormula 1a and Formula 1b.

[0021] The above compound of Formula 1a is preferablyN,N,N′,N′-tetramethyl-1,8-naphthalenediamine orN,N′-dimethyl-1,8-naphthalenediamine, and the above compound of Formula1b is preferably N,N,N′,N′-tetramethyl-1,8-diaminofluorene orN,N′-dimethyl-1,8-diaminofluorene.

[0022] These compounds are proton sponges which have very strongbasicity, having pKa ranging from about 12 to about 16. They controldiffusion of acid effectively by being added into photoresistcompositions.

[0023] That is, they prevent the acid generated in the exposed area frombeing diffused into the unexposed area by absorbing the acids. As aresult, excellent profiles can be obtained after developing becausephysical property of photoresist of unexposed region doesn't change.

[0024] In addition, another aspect of the present invention provides aphotoresist composition comprising (i) additive represented by the aboveFormula 1 for preventing acid diffusion; (ii) a base resin (iii) aphotoacid generator; and (iv) an organic solvent.

[0025] The amount of additive of Formula 1 ranges from about 1 to about10% by mole of the photoacid generator employed.

[0026] Any of the customary base resins (photoresist polymers),photoacid generators and organic solutions which are added into theconventional chemical amplification type photoresist composition, can beused. Some of them are disclosed in U.S. Pat. No. 5,212,043 (May 18,1993), WO 97/33198 (Sep. 12, 1997), WO 96/37526 (Nov. 28, 1996), EP 0794 458 (Sep. 10, 1997), EP 0789 278 (Aug. 13, 1997), U.S. Pat. No.6,132,926 (Oct. 17, 2000), U.S. Pat. No. 6,143,463 (Nov. 7, 2000), U.S.Pat. No. 6,150,069 (Nov. 21, 2000), U.S. Pat. No. 6,180,316 B1 (Jan. 30,2001), U.S. Pat. No. 6,225,020 B1 (May 1, 2001), U.S. Pat. No. 6,235,448B1 (May 22, 2001) and U.S. Pat. No. 6,235,447 B1 (May 22, 2001).

[0027] Typically, the base resin has ring structure having thecycloolefin back bone. It is preferable that the base resin comprisesrepeating unit prepared by radical additional polymerization ofcycloolefin comonomers with functional groups and the ring structures ofthe cycloolefin comonomers remains in the main chain of repeating unit.The functional groups are acid labile group which has effect oninhibition dissolution of base resin and carboxylic group.

[0028] More preferably, the base resin comprises cycloolefin comonomerwith hydroxy alkyl functional group in order to improve adhesiveness towafer and control sensitivity.

[0029] An exemplary base resin comprises repeating unit represented bythe following Formula 2. The repeating unit comprises 2-hyroxyethylbicyclo[2,2,1]hept-5-ene-2-carboxylate (m=1) or 2-hydroxybicyclo[2,2,2]oct-5-ene-2-carboxylate (m=2) in order to improveadhesiveness to wafer.

[0030] wherein, a:b:c:d is 30-50 mole %:20-50 mole %:1-30 mole %:1-45mole % and m is 1 or 2.

[0031] Preferred photoacid generators are diazomethan derivatives,glyoxym derivatives and benzyltosylate derivatives which have low lightabsorbance at 193 nm and 248 nm wavelength, for examplephthalimidotrifluoromethane sulfonate, dinitrobenzyltosylate, n-decyldisulfone, naphthylimido trifluoromethane sulfonate or mixtures thereofare preferably used. And sulfide type compound or onium type compoundwhich also have low light absorbance at 193 nm and 248 nm, for examplediphenyl iodide hexafluorophosphate, diphenyl iodide hexafluoroarsenate,diphenyl iodide hexafluoroantimonate, diphenyl p-methoxyphenylsulfoniumtriflate, diphenyl p-toluenylsulfonium triflate, diphenylp-isobutylphenylsulfonium triflate, triphenylsulfoniumhexafluorophosphate, triphenylsulfonium hexafluoroarsenate,triphenylsulfonium hexafluoroantimonate, triphenylsulfonium triflate,dibutylnaphthylsulfonium triflate or mixtures thereof are also used forphoto acid generator.

[0032] The amount of photoacid generator ranges from about 0.05 to about10% by weight of the base resin employed. It has been found that whenthe photoacid generator is used in the amount less than about 0.05%, itlowers photosensitivity of the photoresist composition, and when thephotoacid generator is used in the amount greater than about 10%, itresults in a poor pattern formation due to its high absorption.

[0033] On the other hand, preferred organic solvents for photoresistcomposition are methyl 3-methoxypropionate, ethyl 3-ethoxypropionate,propylene glycol methyl ether acetate, cyclohexanone, 2-heptanone, ethyllactate or mixture thereof.

[0034] The amount of organic solvent ranges from about 200 to about1000% by weight of the photoresist polymer to coat the photoresist in awanted thickness. It has been found that when the organic solvent isused in the amount of 500 wt %, a thickness of the photoresist is about0.51 μm.

[0035] A process for forming a photoresist pattern comprises:

[0036] (a) coating the photoresist composition described above on awafer to form a photoresist film;

[0037] (b) exposing the photoresist film to light using an exposer; and

[0038] (c) developing the exposed photoresist film to obtain aphotoresist pattern.

[0039] The process for forming the photoresist pattern can furtherinclude a soft baking which is performed before the step (b) and/or apost baking step which is performed after the step (b). Preferably, thesoft and post baking steps are performed at a temperature ranging fromabout 70 to about 200° C.

[0040] Exemplary light sources which are useful for forming thephotoresist pattern include VUV (157 nm), ArF (193 nm), KrF (248 nm),E-beam, EUV (13 nm), ion beam or X-ray. Preferably, the irradiationenergy in the step (b) ranges from about 0.1 mJ/cm² to about 50 mJ/cm².

[0041] On the other hand, the step (c) can be performed in alkalinedeveloping solution which is preferably a TMAH aqueous solution with aconcentration ranging from about 0.01 to about 5 wt %.

[0042] Semiconductor devices can, of course, be manufactured using thephotoresist compositions described above.

[0043] The disclosed compounds and photoresist compositions containingthe same will now be described in more details by referring to examplesbelow, which are not intended to be limiting.

EXAMPLE 1 Preparation of Photoresist Compositions and Formation of FIG.(1)

[0044] To 100 g of propylene glycol methyl ether acetate was added 10 gof compound of Formula 2 (wherein m=1) as a base resin, 0.006 g ofN,N,N′,N′-tetramethyl-1,8-naphthalenediamine as an additive and, 0.06 gof phthalimidotrifluoromethane sulfonate and 0.06 g oftriphenylsulfonium triflate as photoacid generators. The resultingmixture was stirred and filtered through 0.20 μm filter to obtain aphotoresist composition.

[0045] The photoresist composition thus prepared was spin-coated on abare silicon wafer to form a thin photoresist film, and soft-baked at140° C. for 90 seconds. After soft baking, the photoresist was exposedto light using a ArF laser exposer, and then post-baked at 140° C. for90 seconds. When the post-baking was completed, it was developed in 2.38wt % aqueous TMAH solution for 40 seconds, to obtain 0.11 μm L/Sphotoresist pattern. As a result, optimum irradiation energy was 13mJ/cm² and LER was 9.4 nm (see FIG. 1). 160 nm of randomly-selectedpattern length was divided into 32 points, and critical dimension ofeach point was measured using Hitach SEM 8840 (□120K), and LER wasdetermined as 3σ (wherein σ is standard deviation).

EXAMPLE 2 Preparation of Photoresist Compositions and Formation of FIG.(2)

[0046] The procedure of Example 1 was repeated using 0.006 g ofN,N′-dimethyl-1,8-naphthalenediamine instead of 0.006 g ofN,N,N′,N′-tetramethyl-1,8-naphthalenediamine to obtain the pattern of0.11 μm L/S pattern. As a result, optimum irradiation energy was 10.5mJ/cm² and LER was 13 nm (see FIG. 2).

EXAMPLE 3 Preparation of Photoresist Compositions and Formation of FIG.(3)

[0047] The procedure of Example 1 was repeated using 0.006 g ofN,N,N′,N′-tetramethyl-1,8-diaminofluorene instead of 0.006 g ofN,N,N′,N′-tetramethyl-1,8-naphthalenediamine to obtain the pattern of0.11 μm L/S pattern. As a result, optimum irradiation energy was 15mJ/cm and LER was 12 nm (see FIG. 3).

EXAMPLE 4 Preparation of Photoresist Compositions and Formation of FIG.(4)

[0048] The procedure of Example 1 was repeated using 0.006 g ofN,N′-dimethyl-1,8-diaminofluorene instead of 0.006 g ofN,N,N′,N′-tetramethyl-1,8-naphthalenediamine to obtain the pattern of0.11 μm L/S pattern. As a result, optimum irradiation energy was 11mJ/cm² and LER was 11.6 nm (see FIG. 4).

COMPARATIVE EXAMPLE 1 Preparation of Photoresist Compositions andFormation of FIG. (5)

[0049] The procedure of Example 1 was repeated using 0.006 g oftrioctylamine instead of 0.006 g ofN,N,N′,N′-tetramethyl-1,8-naphthalenediamine to obtain the pattern of0.11 μm L/S pattern. As a result, optimum irradiation energy was 16.7mJ/cm² and LER was 14.3 nm (see FIG. 5).

COMPARATIVE EXAMPLE 2 Preparation of Photoresist Compositions andFormation of FIG. (6)

[0050] The procedure of Example 1 was repeated without any additive toobtain the pattern of 0.12 μm L/S pattern. As a result, optimumirradiation energy was 37.4 mJ/cm² and LER was 16 nm or more (see FIG.6).

[0051] As discussed earlier, photoresist compositions comprising anadditive according to this disclosure can effectively prevent aciddiffusion even if the additive is used in low concentrations. Use of theadditives disclosed herein improve LER, result in improved profiles andlower the optimum irradiation energy.

What is claimed is:
 1. A photoresist composition comprising aphotoresist additive for preventing acid diffusion, wherein the additiveis represented by Formula 1:

wherein, R₁, R₂, R₃ and R₄ are individually selected from the groupconsisting of H, linear C₁-C₁₀ alkyl and branched C₁-C₁₀ alkyl, and k is0 or
 1. 2. The composition according to claim 1, wherein the additive isselected from the group consisting ofN,N,N′,N′-tetramethyl-1,8-naphthalcnediamine,N,N′-dimethyl-1,8-naphthalenediamine,N,N,N′,N′-tetramethyl-1,8-diaminofluorene andN,N′-dimethyl-1,8-diaminofluorene.
 3. A photoresist compositioncomprising the additive of claim 1, a base resin, a photoacid generatorand an organic solvent.
 4. The photoresist composition according toclaim 3, wherein the additive is present in an amount ranging from about0.5 to about 20% by weight of the photoacid generator.